UREI 6500 issues

[hamrules]

I got this amp and I replaced a few resistors that were wrong from someone else so both boards are correct and identical and the caps on the control boards too. One control board after turning on lights up the normal led and the clip led stays on and the output relay closes. It does this for either amp module it’s hooked to. The other control board after turning on lights up the normal led, the clip led goes off and the relay closes. Then after 30 seconds the relay starts to open and close constantly along with the clip led lighting up and off. It does this for either amp module it’s hooked to. I’m not sure what to look for to figure this out. Should I check all the output devices to see if any show bad, there’s 14 per module. The only thing I have is the circuit drawing from the JBL site.

 

[avionic]

The only thing I have is the circuit drawing from the JBL site.

A link would be handy.

 

[hamrules]

Here's the link to the file: jblproservice.com/pdf/Vintage JBL-UREI Electronics/UREI-6500.pdf

 

[avionic]

One control board after turning on lights up the normal led and the clip led stays on and the output relay closes.

Does this channel work?

 

[avionic]

I got this amp and I replaced a few resistors that were wrong from someone else so both boards are correct and identical and the caps on the control boards too.

Was this amp working or non-working before you started?

 

[hamrules]

Does this channel work?

I have not hooked it up to a speaker but it does show 12.8mv DC offset at the speaker terminal.

 

[hamrules]

Was this amp working or non-working before you started?

I bought it and they said it was working but i'm doubtful it really was. I did not actually try it first, maybe I should have.

 

[avionic]

I have not hooked it up to a speaker but it does show 12.8mv DC offset at the speaker terminal.

Thats hardly any DC offset.

 

[hamrules]

I have not hooked it up to a speaker but it does show 12.8mv DC offset at the speaker terminal.

If I move the control board to the other amp channel then it does this identical thing and has 13.0mv DC offset at the speaker terminal.

 

[avionic]

Can you post photos of the parts you replaced on the channel that the relay toggles on and off ?

 

[hamrules]

Can you post photos of the parts you replaced on the channel that the relay toggles on and off ?

I will shoot some pics and get them up later on.

 

[avionic]

If I move the control board to the other amp channel then it does this identical thing and has 13.0mv DC offset at the speaker terminal.

Guess that narrows it down to the control board.

 

[hamrules]

1st is an amp board
2nd is a control board
3rd is the other control board
I didn't take a pic of the other amp board

I was checking the resistors and there seems to be a huge variance in readings on what some of them should be and from control board to control board for the same one on some of them. I'm thinking maybe that's the issue.

 

[avionic]

Compare voltages on IC1 pin 14 on both channels.

 

[hamrules]

Compare voltages on IC1 pin 14 on both channels.

OK. I can see why, now that you said that. I will have to figure out how though as there is no access once they are plugged into the case. No bottom that opens at all.

 

[avionic]

OK. I can see why, now that you said that. I will have to figure out how though as there is no access once they are plugged into the case. No bottom that opens at all.

Tack a test wire to the pins on the solder side.

 

[avionic]

IC1 is one of those two socketed chips. Should be accessible from the top side. Just be extremely careful not to short out adjacent pins with your test probe.

 

[avionic]

TL084CN

 

[avionic]

What part number is printed on those chips?

 

[avionic]

Just be extremely careful not to short out adjacent pins with your test probe.

Put a piece of heat-shrink tubing or electrical tape over the probe tip. Leaving just the very point exposed.